1. Field of the Invention
This invention relates to a production method for a crystal glass composition which looks like or can be regarded as crystal glass although it does not contain lead (Pb).
2. Description of the Related Art
Conventionally, lead-containing crystal glass is used popularly as crystal glass for use to produce tableware or like articles. The characteristics of it, in short, such characteristics that "it is massive", that "it has a high light refractive index and exhibits a high dispersion value of light" and that "it melts readily", are provided principally by PbO. While the content of PbO varies widely, it generally ranges from 24 to 26 percent by weight.
Since lead-containing crystal glass contains much lead having a high toxicity in this manner, where it is used for tableware, injuries to the human bodies are apprehended. Thus, the regulations to the content of PbO tend to become further severe.
Therefore, the assignee of the present invention has proposed, in Japanese Patent Laid-Open Application No. Heisei 6-183774, a glass composition which does not contain lead at all but has characteristics equivalent to those of lead-containing crystal glass. The glass composition consists of SiO.sub.2, TiO.sub.2 for assuring a high light refractive index and a high dispersion, BaO for assuring a high density and a high refractive index, K.sub.2 O for suppressing development of a color by Fe ions and Na.sub.2 O for decreasing the melting temperature as principal components.
However, since the glass composition employs TiO.sub.2 (titanium oxide) as a raw material substituted for PbO, the glass has a tendency to be colored yellowish due to coexistence of TiO.sub.2 with an impurity originating from the raw material.